Governor-controlled electric motors having a commutator



April 11, 1967 J, P. WREN 3,313,963

GOVERNOR'CONTROLLED ELECTRIC MOTORS HAVING A COMMUTATOR Filed June 23, 1964 Fig.2. 1a

United States Patent 3,313,963 GOVERNOR-CONTROLLED ELECTRIC MOTORS HAVING A COMMUTATOR John Pelham Wren, Chiseldon, Swindon, England, assignor to Garrard Engineering Limited, Swindon, England, a British company Filed June 23, 1964, Ser. No. 377,422 Claims priority, application Great Britain, June 27, 1963, 25,675/63 7 Claims. (Cl. 31068) This invention relates to direct-current motors for use at low voltages and is particularly intended for use in the drives of battery-operated gramoph'one record players and record changers and similar apparatus, although it is also suitable for other uses in which a substantially constant running speed within a range of supply voltages is required. The invention is concerned with motors of the kind having an armature equipped with a commutator and including, in order to keep their speed substantially constant, a centrifugally operated switch in one or more of the winding circuits controlled by the individual commutator segments, with or without a resistor by-passing the switch contacts. The present invention has for an object to provide an improved motor of the kind specified which is capable of achieving good constancy of speed and lends itself to convenient achievement of static and dynamic balance.

According to the invention in its broadest aspect, two or more centrifugally operated switches are arranged, together with any required balance weight, on a governor disc, which is coaxial with the armature axis. In the case of two switches, these switches as well as the contact brackets and resistor elements associated with the two switches are preferably arranged in mutually diametrically opposite pairs so that all masses are substantially balanced in a common plane at right angles to the rotor axis without the need for a separate balance weight. Preferably the disc is formed with a number of perforations uniformly distributed on a circle about its axis, so that any minor unbalance caused, for example, by differences in the amount of solder used at individual connections, can be balanced in substantially theirown plane by weight pins inserted in one or more of the holes.

According to a preferred form of the invention the commutator is of plane construction and comprises a number of segments, for example three segments mounted upon the outer face of the disc so that any unbalance due to the connections to the commutator segments will occur in substantially the same plane as any unbalance due to the construction and connection of the governor, thus permitting all resultant centrifugal unbalance to be balanced statically and dynamically by adding a Weight pin of suitable weight at one point of the disc, which is made of insulating material.

In order that the invention may be more readily understood, the armature or rotor of a motor incorporating one form of the invention will now be described in more detail'with reference to the accompanying drawing, which is identical with the drawing accompanying the provisional specification, and in which FIGURE 1 is a perspective view, and

FIGURE 2 is a circuit diagram.

Referring now first to FIGURE 1, the rotor comprises a three-pole magnetic armature I mounted on a rotor shaft 2 and carrying armature windings 1a. All these parts are constructed to be symmetrical about the shaft and thus to be substantially inherently balanced. Attached to one end of the armature 1 is a disc 3 of insulating material, for example phenolformaldehyde syntheticresin material. This disc is also symmetrical about the shaft 2, and three commutator segments 21, 22 and 23 3,313,963 Patented Apr. 11, 1967 are formed on it by attaching to the disc a suitably shaped plate of silver-alloy-plated copper and then sub-dividing the plate by radial cuts 24 into the three segments to which respectively corresponding ends of the windings 3 associated with each of the rotor poles, are attached. The other ends of the windings are interconnected and shown in FIGURE 2 by two connection lines each including a switch whose contacts are by-passed by a resistor, the two resistors being shown at 18 and 19 in FIGURE 1. Each of the switches has a movable contact mounted on a spring blade 16 and 17 respectively, which carries a centrifugal weight 16a or 17a and which co-operates with an adjustable fixed contact arranged at the end of a set screw 14 or 15. The set screw 14 engages screw threads of a contact bracket 4, which is hereinafter referred-to as combination bracket, and to an extension of which the governor spring 16 is attached, while the screw threads engaged by screw 14 are in a second contact bracket 8, which is separated by a gap 8a from the spring bracket 9 to which the other governor spring 17 is secured. The contact-screw bracket 8 is secured to the disc 3 by two rivets 10 and 11, and two further rivets 12 and 13 secure the balance-spring bracket 9 two rivets 6 and 7 are sufii-.

cient to support the combination bracket 4 which supports both the second contact screw 14 and the second balance spring 16. The extra weight of the two additional screws required at the opposite side of the shaft is balanced by a balance weight 5, which is secured to the disc by the rivet 5, the same rivet also secures one end of the combination bracket. It has been found that with modern methods of mass-production a rotor constructed in this manner will generally be sufficiently balanced statically'and dynamically for satisfactory use in a gramophone drive, but in order to permit any residual unbalance of the governor and commutator to be balanced statically and dynamically in the simplest possible manner, a set of axial bores 20 are uniformly distributed around the periphery of the disc 3, thus allowing pinshaped weights, the effect of which may be varied by using pins of greater or less length, to be inserted into that one of the holes 20 which is substantially diametrically opposite to the resultant unbalance. Since all elements liable to cause unbalance, such as the solder connections to the resistors, the commutator segments, and the contact brackets, are approximately in the plane of the disc 3, there is substantially no danger of an appreciable dynamic unbalance once static balance has been achieved. In practice the set screws 14 and 15 are so adjusted that the two switches open at slightly different rates of revolution, thus ensuring, in conjunction with the resistors 18 and 19, a smooth governing action within a comparatively wide range of torques and/ or alterations of the input voltage, the desired balance between sensitivity of speed maintenance and voltage and torque range in which the governor is effective, being ensured by suitable choice of the values of the resistors 18 and 19.

What I claim is:

1. In a constant speed electric motor, comprising an armature body having journals mounted for rotation, armature windings on said body, a disc secured to said armature body coaxially thereto for joint rotation therewith, the said disc having two major surfaces, a plurality of substantially flat commutator segments secured in mutually electrically insulated relation on one of said major surfaces of said disc,'said elements being connected to said armature windings to constitute a commutator for said windings, at least two centrifugal switches of equal inertial mass mounted on said disc at equal radial distances from the journal axis and uniformly spaced therearound, said switches being arranged to open respectively at different speeds of rotation and being so connected each in one of the winding circuits controlled by the commutator segments as to decrease, the effective armature torque in progressive stages as each switch opens.

2. An electric motor as claimed in claim 1, wherein said disc is made of insulating material.

3. An electric motor as claimed in claim 2, wherein said commutator segments are adhesively secured to said one major surface of the disc.

4. An electric motor as claimed in claim 2, wherein two such switches are provided and arranged in mutual dia- 10 metric opposition, each switch being included in a diflen ent winding circuit.

, 5. An electric motor as claimed in claim 1, further including a number of resistors equal to the number of said switches and connected to respectively by-pass said switches.

6. An electric motor as claimed in claim 5, wherein said resistors are mounted on said disc and are uniformly spaced around the journal axis at equal radial distances therefrom.

4 7. A motor as claimed in claim6, wherein the disc is formed with a number of perforations of equal size uniformly distributed in a circle about the journal axis.

References Cited by the Examiner UNITED STATES PATENTS 647,155 5/l90'O Richards 31068 1,249,526 12/1917 Shelton 310-68 2,165,858 7/1939 Jepson 310-68 2,281,711 5/1942 Peck 31068 FOREIGN PATENTS 212,444 12/ 1960 Austria. 1,131,779 6/1962 Germany.

948,445 9/ 1960 Great Britain.

MILTON O. HIRSHFIELD, Primary Examiner.

J. D. MILLER, Assistant Examiner. 

1. IN A CONSTANT SPEED ELECTRIC MOTOR, COMPRISING AN ARMATURE BODY HAVING JOURNALS MOUNTED FOR ROTATION, ARMATURE WINDINGS ON SAID BODY, A DISC SECURED TO SAID ARMATURE BODY COAXIALLY THERETO FOR JOINT ROTATION THEREWITH, THE SAID DISC HAVING TWO MAJOR SURFACES, A PLURALITY OF SUBSTANTIALLY FLAT COMMUTATOR SEGMENTS SECURED IN MUTUALLY ELECTRICALLY INSULATED RELATION ON ONE OF SAID MAJOR SURFACES OF SAID DISC, SAID ELEMENTS BEING CONNECTED TO SAID ARMATURE WINDINGS TO CONSTITUTE A COMMUTATOR FOR SAID WINDINGS, AT LEAST TWO CENTRIFUGAL SWITCHES OF EQUAL INERTIAL MASS MOUNTED ON SAID DISC AT EQUAL RADIAL DISTANCES FROM THE JOURNAL AXIS AND UNIFORMLY SPACED THEREAROUND, SAID SWITCHES BEING ARRANGED TO OPEN RESPECTIVELY AT DIFFERENT SPEEDS OF ROTATION AND BEING SO CONNECTED EACH IN ONE OF THE WINDING CIRCUITS CONTROLLED BY THE COMMUTATOR SEGMENTS AS TO DECREASE, THE EFFECTIVE ARMATURE TORQUE IN PROGRESSIVE STAGES AS EACH SWITCH OPENS. 